This invention relates to combined refrigeration and heating circuits.
The molding of thermoplastic raw material involves the heating up of the raw material to the molding temperature, often with preliminary drying, and the subsequent cooling of the molded product. It is clearly uneconomic to have the heating and drying systems separate from the chilling system. Moreover, separate chilling plant poses the problem of what to do with the extracted heat. Use of a cooling tower raises in turn problems of corrosion, biological growth and scale formation, while the wasteful use of mains water for cooling is prohibited by most water authorities, as is the disposal of heated water into rivers or drainage systems. Air cooling solves many of these problems and is now widely employed.
Clearly, however, the consumption of energy for heating and drying the plastics raw material and the subsequent disposal of heat from the chilling plant is wasteful and the utilization of the exhaust heat is desirable.
One problem that arises from the utilization of heat taken from the condenser of a chilling system is that of inadequate cooling of the condenser for efficient operation of the chilling system if insufficient heat is being taken from the system utilizing the extracted heat.
Our earlier UK Application No. 2 067 275 A solved this problem by providing sensing means for sensing when insufficient heat was being taken from the condenser to permit condensation of all the refrigerant passing therethrough and cooling means responsive to said sensing means for additionally cooling the refrigerant to ensure complete condensation thereof.
However, not only is the amount of heat recovered important, but also its quality, i.e., its temperature. Our earlier system, because of the limitations imposed by the requirements of efficient condensation, could not deliver air or water heated by the condenser to a temperature of more than 60.degree. C., the maximum operating temperature of the condenser. While such a temperature is suitable for many applications it is desirable for some other applications to have available a heat transfer fluid heated to temperatures of up to 90.degree. C. It is also air at this temperature that is required for many heating and drying applications in thermoplastic molding processes.